Many methods have been developed to generate 3-D images. These methods differ from two dimensional display technologies such as photography and television in that they deliver laterally displaced images of a subject to a viewer's eyes. The viewer synthesizes three-dimensional experience of objects and space from these slightly displaced views. Many methods deliver a specific pair of images, one to each eye. With these methods the viewer is confined to looking at the subject from a predetermined position for a particular stereo effect. In contrast, holography, lenticular screen, and rastor display methods enable many viewing angles of a subject.
Holography is significantly different from other methods of three-dimensional imaging. Because holography requires the use of coherent light sources such as lasers to store interference patterns of light, it is color and scale limited, and complex to practice relative to lenticular and rastor methods.
Lenticular screen methods utilize ordinary light sources to record and display a 3-D image. Different views of a subject are interlaced and laminated behind an array of semi-cylindrical lenticular lenses. Interlacing is the process of placing together images that have been recorded from different viewing positions in thin parallel linear strips (or lineations), usually through the use of a black line rastor or lenticular screen. The resultant interlaced pattern of images is then placed behind the lenticular lenses at their focal distance so that only one lineation is visible through each lens from any particular viewing angle. Each eye sees different lineations (which represent corresponding distinct views of the original subject) and consequently people looking at the display can construct three dimensional images in their minds.
Lenticular screen images are limited in terms of clarity and resolution, but more importantly, because of the geometric properties of their optics, many viewing zones result. A slight shift in viewing position will often present the viewer with lineations from the adjacent grouping. The result is a pseudoscopic or compromised effect.
Rastor methods of three dimensional display are capable of higher quality results. As with lenticular screens, different views are interlaced in parallel lineations but, rather than displaying this interlaced pattern behind a lenticular screen, it is presented behind a black line rastor. The rastor is formed of parallel lineations which are alternately clear and dark. The widths of these clear and dark lineations can be adjusted to reduce the viewing zone "jump" that is intrinsic to lenticular optics. However, the use of opaque lineations reduces the amount of light that illuminates the interlaced pattern behind it, so back-lighting is employed. This enables the interlaced pattern to be viewed through the slits in the rastor so that individual images are visible from different viewing angles. This produces the three dimensional effect.
Prior art rastor displays have produced satisfactory images for viewing. However, they have not solved problems of viewing in bright ambient lighting conditions or extreme image dislocation at the viewing transition point between groupings of lineations. In addition, they usually required means to illuminate the structure from behind the image.